Many electronic systems interface with one or more external components to effectuate their purpose. Often, such external components are sensors that respond electrically to some preselected monitored event. In some systems, assured receipt of accurate sensor information can be critical to overall operation of the system. For instance, electronic engine controls as used to control internal combustion engines require accurate and timely engine position information. Cam position or flywheel position sensors are utilized to provide an electric signal that relates to the position of the relevant engine component. If the sensor fails, however, the electronic engine control will typically not operate effectively. Hence, loss of the sensor signal can be highly disabling.
To mitigate this sensitivity, redundant sensors are often used when lack of sensor information might significantly disable a system. This solution, however, gives rise to a new problem. The system receiving the redundant signals must be able to decide which sensor input to use and must further have some means of determining when and if sensor information appears unreliable to the extent that the data should be ignored.
Pursuant to one prior art solution to the latter problem, the system will use the information from one sensor as a default condition, while simultaneously monitoring a second redundant sensor signal (see FIG. 3). If and when the first sensor fails to provide a signal at the same time that the second sensor provides a signal (for example, see FIG. 6), the system will presume a fault on the first sensor line and utilize instead the signal from the second sensor.
Unfortunately, the above solution gives rise to yet another problem. Redundant signals often exhibit skew; that is, the leading and trailing edges of the redundant signals may vary from one another in time (for example, see FIG. 4). If such skew occurs, the prior art technique may conclude that a fault condition exists when in fact it does not.
There therefore exists a need for a device that can process redundant signals and provide an appropriate output based thereon. This device should monitor all signal inputs for fault conditions, and should have logic capabilities that enable the device to use only inputs that have not faulted. Further, such a device should have a degree of skew insensitivity to prevent at least some unnecessary fault condition responses. The degree of insensitivity should be selectively variable. Finally, such a device should be relatively inexpensive to manufacture and implement, and reliable in operation.